Potatoes and other tubers, vegetables, crops and produce are typically held in large storage facilities after harvest to maintain quality and provide a uniform supply of product to market. Modern potato storage facilities, for example, can often hold more than 20,000 tons of potatoes in piles as high as 20 feet. These piles, however, can generate considerable heat from respiration of the potatoes. One ton of stored potatoes, for example, can generate about 2 BTUs of heat per day. For this reason, conventional storage facilities typically include ventilation systems for cooling the potatoes. In addition, these facilities typically include systems for controlling the air temperature and humidity to prevent excessive dehydration, decay, and the development of high sugar concentrations in the potatoes. Table potatoes, for example, are typically stored at about 40°-45° F. and about 95% relative humidity, while potatoes for making chips or French fries are typically stored at about 45-55° F. and about 95% relative humidity. Maintaining the humidity in potato storage facilities at, e.g., above 90% can significantly reduce shrinkage and corresponding profit losses.
Conventional potato storage facilities typically include a series of vents or other openings on an exterior wall for introducing outside air into the facility. This air can be cooled and/or conditioned to increase the moisture content by moving the air through an air cooler (e.g., an evaporative cooler), a humidifier, and/or other known air conditioning devices, and then directed through a series of ventilation ducts or pipes that extend underneath the pile of potatoes. The ducts are perforated along their lengths to allow the cool, moist air to flow out and upwardly through the potatoes, cooling the potatoes and preventing excessive dehydration. The air is warmed as it flows through the potatoes, and after flowing through the pile it is typically exhausted through one or more vents in an exterior wall of the facility.
Although it can be important to maintain stored potatoes in a humid environment to reduce shrinkage, it is also desirable to keep the potatoes dry to reduce the formation of rot. One challenge associated with conventional potato storage facilities, however, is that in relatively moderate or cool climates the heated and humid air rising off the pile of potatoes can condense on ceiling panels above the potatoes. This can happen when, for example, the outside air temperature is low enough to cool the ceiling panels below the dew point of the air inside the facility. The condensation on the ceiling panels can form water droplets that fall onto the potatoes, inducing rot.
Some conventional storage facilities have attempted to address the condensation problem by heating the ceiling surfaces above the dew point with warm air from conventional gas, oil or electric heating sources. This approach, however, adds cost for operating and maintaining the heating equipment. Other storage facilities attempt to thermally insulate the ceiling panels by covering them with insulation, such as spray-on urethane insulation. Over time, however, the insulation can degrade and crack, allowing moisture to form. Moreover, the insulation may off-gas or otherwise deteriorate over time, raising concerns about product contamination. Because of the difficulties and/or cost of implementing conventional techniques for reducing water formation, some storage facility operators have simply resorted to reducing the humidity of the cooling air to avoid condensation. But reducing the humidity can lead to the undesirable result of potato dehydration and shrinkage, with a corresponding reduction in yield and lost profits.